Fix incorrect argument type in sscanf

    clang -Os -DNDEBUG -std=c11 -DVERSION='"0.2.0-4-g073eced"' -o build/tty-copy.o -c tty-copy.c
    tty-copy.c:256:13: warning: passing 'uchar [16]' to parameter of type 'const char *' converts between pointers to integer types with different sign [-Wpointer-sign]
            if (sscanf(buf, "\033[%d;%dR", &row, &col) != 2) {
                       ^~~
    /usr/include/stdio.h:412:60: note: passing argument to parameter '__s' here
    extern int __REDIRECT_NTH (sscanf, (const char *__restrict __s,
                                                               ^
    1 warning generated.

Fixes #3

tty-copy.c

@@ -240,7 +240,7 @@ static int fpeek (FILE *stream) {
  * Returns the cursor position on the X-axis (column), or -1 on error.
  */
 static int get_cursor_column (FILE *tty) {
-	uchar buf[16] = {'\0'};
+	char buf[16] = {'\0'};
 
 	if (fputs("\033[6n", tty) < 0) {
 		return -1;